Method For Rolling A Sheet Metal Strip

ABSTRACT

A method is provided for controlling cold rolling of a sheet metal strip involving continuously passing the strip in at least two successive rolling stands, each stand including at least two driven rolls between which the strip moves and is plated. The method includes estimating the sliding variation in output of one rolling stand; and correcting the rotation speed of the rolls of at least one corrected rolling stand based on the estimated sliding variation.

The present invention relates to a method for cold rolling a sheet metalstrip.

BACKGROUND

Cold rolling is an important stage in the production of long products inthe metallurgy industry. Its objective is to reduce the thickness of theproduct input. The sheet metal products are usually destined for themotor vehicle and foodstuffs industries.

The rolling thus consists of reducing the thickness of a metal strip bymeans of plastic deformation. For this purpose, the strip circulatescontinuously between two rotating rolls, known as work rolls, withparallel axes, which delimit between one another a gripping space whichis commonly known as an air gap, and to which force is applied. Thereduction of thickness of the strip is then obtained by compression.This device constitutes a stand of a rolling mill. The use of aplurality of stands in succession into which the strip passessimultaneously constitutes a rolling mill tandem.

The work rolls are rotated at a regular speed. As it passes into thestands of the rolling mill, the speed of the strip increases, takinginto account the decrease in its thickness and the maintaining itswidth.

For metallurgical reasons, the variations of thickness at the outputfrom the tandem must be as slight as possible. For this purpose,different regulation loops are used.

Thus, it is common to continuously measure the linear speed of the stripoutput from the first stand, the thickness of the strip input into, andoutput from the first stand, and the thickness output from the finalstand.

For example, it is known to correct the thickness by acting on the airgap of the work rolls of the first stand according to the thicknessmeasured at the input of the first stand. The air gap is the distancewhich separates the two work rolls.

Similarly, it is known to modify the air gap of the work rolls of thefirst stand according to the thickness measured at the output from thisfirst stand.

It is also known to modify the speed of rotation of the rolls of thefirst stand according to the thickness of the strip output from thefirst stand.

Finally, it is known to adjust the speed of rotation of the rolls of thefinal stand on the basis of the thickness measured at the output fromthis final stand.

These correction methods permit reduction of the variations of thicknessof the strip, but remain insufficient to take into account complexphenomena which occur in a rolling mill.

In addition, in the particular context of hot rolling, a method is knownfrom document EP-A1-0 000 454 for compensation for the effects ofvariation of sliding on the traction between stands, so as to maintainthis traction at a constant value in order to maintain the width of therolled product. This method is based on the principle of maintaining thespeed of the strip at the two ends between stands.

Within the context of cold rolling, the physical phenomena involved aredifferent. Thus, the traction between stands does not have any effect onthe width of the rolled product. Consequently the problem of maintainingthe traction between stands at a constant value solved by the methoddescribed in document EP-A1-0 000 454 is not important within thecontext of cold rolling. In addition, the matter of controlling thetraction of the strip in a cold rolling installation is easily resolvedby regulating traction using tractiometers. These devices are generallynot used during hot rolling of a metal sheet, since they are verydifficult to implement.

It is also usual, in cold rolling mills, to allow the traction betweenstands to increase naturally when the rolling speed decreases. Contraryto the hot rolling methods (where the traction is kept constant) it isthis variation of traction between stands which gives rise to variationof sliding at the output from the stand upstream.

SUMMARY OF THE INVENTION

An object of the invention provides a cold rolling method which makes itpossible to reduce further still the variations of thickness of thestrip at the output from the rolling mill.

The invention provides a method for controlling the cold rolling of asheet metal strip of the aforementioned type, characterised in that itcomprises:

-   -   estimating the variation of sliding at the output from a stand;        and    -   correcting the speed of rotation of the rolls of at least one        stand, corrected in accordance with the estimated variation of        sliding.

According to particular embodiments, the method may include one or moreof the following features;

-   -   the estimation of the variation of sliding comprises a step of        measuring the linear speed of the strip at the output from the        stand, a step of estimating the circumferential speed of the        rolls in the stand, and a step of calculating the sliding of the        strip on the basis of the linear speed of the strip at the        output from the stand and the circumferential speed of the rolls        of the stand;    -   the variation of sliding is estimated for the first stand,        taking into consideration the direction of circulation of the        strip;    -   the correction of speed is applied to a set of at least two        successive stands, taking into consideration the direction of        circulation of the strip;    -   the corrections of speed applied to the successive stands are        identical;    -   the correction of speed comprises varying the speed of the stand        which is corrected substantially when estimating the variation        of sliding;    -   the correction of speed comprises varying the speed of the first        stand corrected with temporal offsetting which is equal to the        time of transfer of the strip between the final corrected stand        and the following stand, taking into consideration the direction        of circulation of the strip;    -   the temporal offsetting incorporates a delay caused by        filtering; and    -   the correction of speed comprises varying the speed of the first        stand corrected with temporal offsetting which is equal to the        time of transfer of the strip between the stand following the        stand where the variation of sliding is estimated and the first        corrected stand, taking into consideration the direction of        circulation of the strip;    -   gripping correction is applied to at least one stand adjacent to        a corrected stand, in order to maintain the traction; and    -   the control of a traction maintenance device situated upstream        from the first stand and the said control takes into account the        estimated variation of sliding.

The invention also provides a device for controlling the rolling of asheet metal strip comprising at least two successive stands, eachcomprising at least two driven rolls between which the strip circulatesand is compressed, characterised in that it comprises:

-   -   means for estimating the variation of sliding at the output from        a stand;    -   means for correcting the speed of rotation of the rolls of at        least one stand corrected in accordance with the estimated        variation of sliding; and    -   means for implementing a method as previously defined.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reading the followingdescription, provided purely by way of example and with reference to thedrawings, in which:

FIG. 1 is a schematic view of a rolling installation according to theinvention;

FIG. 2 is a diagram of the means for compensation for the effect of thevariations of sliding on the thickness, explaining the correction stepsto be implemented according to a first embodiment; and

FIGS. 3 and 4 are views identical to those in FIGS. 1 and 2respectively, of another embodiment.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates schematically an installation 10 for cold rolling ofa metal sheet strip B. Thus, this installation comprises, in a knownmanner, a system 11 for maintaining the traction at the input of therolling mill. This system comprises an uncoiler 12 in the case of areel-to-reel rolling mill, or an S-shaped block in the case of acontinuous rolling mill, the uncoiling speed of which is controlled by aunit 14 for controlling the moment.

The rolling installation to which this invention can be appliedcomprises between two and six stands. By way of example, a descriptionwill be given of an installation consisting of five stands 16A, 16B,16C, 16D and 16E, through which the strip B circulates in succession.

In a known manner, each stand of the rolling mill comprises two workrolls 18 with parallel axes, between which the strip B circulates. Theserolls are rotated by drive motors, the speed of which is regulatedaccording to a predetermined command U_(A), U_(B) which is specific toeach stand. Each stand comprises a hydraulic or electro-mechanicalgripping device 22 which makes it possible to transmit to the two workrolls 18 the rolling force necessary in order for them to assure thepredetermined reduction of thickness. This device 22 assures regulationof the air gap which separates the two rolls 18. The rolling force istransmitted from the device 22 to the work rolls 18 by means of stackingof one or more support rolls 20.

A gauge 24 for gauging the thickness J₀ is disposed upstream from thefirst stand 16A. This gauge 24 can continuously determine the thicknessof the strip B before said strip enters the first stand 16A.

Similarly a second thickness gauge J₁ 26 is disposed at the output fromthe first stand 16A. It can determine continuously the thickness of thestrip B after said strip has been rolled in the stand 16A.

In addition, a sensor 28 for sensing the speed V_(S1) is disposed at theoutput from the first stand 16A. It can continuously determine theinstantaneous linear circulation speed of the strip B at the output fromthe stand 16A. The sensor is formed, for example, by a laservelocimeter.

In a known manner, the gauge 26 is connected to a unit 29 for correctingspeed according to the thickness measured at the output from the firststand 16A.

In a known manner, the motors for driving the rolls 18 of the firststand 16A and the second stand 16B are each controlled by a speedregulator 30A, 30B which can define a speed command for the associatedstand motor. The speed regulator 30A is connected to the speedcorrection unit 29 in order to receive an approximate speed correctionu_(1A) which is used to calculate the command u_(A) applied to the firststand 16A.

The speed regulator 30A receives at its input a theoretical speedu_(tA).

The speed regulator 30B can receive at its input a theoretical speedu_(tB) and at its output it can supply an approximate speed signal u_(B)which is applied to the motor which drives the second stand 16B.

In a known manner, the thickness errors measured by the gauge 24 at theinput of the stand 16A are compensated for by action on the air gap ofthe work rolls 18 of the stand 16A, by means of the gripping device 22.This action modifies the thickness at the output from the stand 16A.

In a known manner, the thickness errors measured by the gauge 26 at theoutput from the stand 16A are also corrected by action on the air gap ofthe work rolls 18 of the stand 16A, by means of the gripping device 22.This action modifies the thickness at the output from the stand 16A.

In a known manner, the thickness errors which are measured by the gauge26 at the output from the stand 16A are corrected at the output from thesecond stand 16B by action on the speed of the first stand 16A. Thisspeed correction is processed by the unit 29 and is applied to the stand16A by the regulator 30A, which can regulate the speed of rotation ofthe work rolls 18 by modifying the speed reference u_(tA) such that:

U _(3A)=(1+u _(1A))*ut _(A).

The speed correction u_(1A) which is associated with the first stand 16Ais supplied to an inertia compensation unit 32, which itself isconnected to the moment-controlling unit 14. On the basis of the speedcorrection u_(1A) and the mechanical characteristics of the strip, theunit 32 can determine the moment which must be imposed on the system 12for maintaining the traction at the input of the rolling mill.

According to the invention, the installation is provided with a unit 34for compensation of the speed of rotation of the work rolls of at leasttwo stands according to a variation of sliding measured at the outputfrom the first stand of the rolling installation.

In the first embodiment illustrated in FIG. 1, the compensation unit 34can modify the speed of rotation of the rolls only of the first stand16A. The unit 34 is connected to the sensor 28 for measuring the speedV_(s1). In addition, sensors 36 for measuring the speed of rotation ofthe drive motors of the rolls are provided on the first stand. Thismeasurement makes it possible to calculate the circumferential speedV_(c1) of the work rolls by means of the ratio:

V _(c1) =π*D _(t1) *N _(t1)

where:

-   -   D_(t1) is the diameter of the work roll    -   N_(t1) is the measuring the speed of rotation of the work rolls.

The unit 34 is connected to these rotation speed sensors. The speed ofthe roll is different from the speed of the strip upstream anddownstream from the roll, because of the variation of thickness of thisstrip during the passage between two rolls and the physical phenomenawhich are associated with the rolling. The speed of the strip is equalto the speed of the roll only at a point of the periphery of the rolldesignated by a neutral point.

The diagram of the compensation unit 34 is illustrated in FIG. 2. Thisunit comprises a module 42 for calculating the sliding of the strip atthe output from the stand 16A, a module 44 for calculating the temporalvariation of sliding of the strip, and a unit 46 for processing a signalfor correcting the speed of rotation only of the rolls of the firststand 16A.

More specifically, the module for calculating the sliding 42 comprises adivider 52 which can assure the division of the linear speed V_(s1) ofthe strip at the output from the first stand 16A by the circumferentialspeed V_(c1) of the rolls of the first stand provided by the sensor 36.

A subtracter 54 subtracts the number 1 from the result of the quotientof the speeds.

Thus, the sliding g₁ is obtained by means of the equation:

$g_{1} = \left( {\frac{V_{s\; 1}}{V_{c\; 1}} - 1} \right)$

where:

-   -   V_(s1) is the linear speed of the strip between the first and        second stands; and    -   V_(c1) is the circumferential speed of the rolls of the first        stand.

The calculation module 42 comprises at its output a filter 58 whichmakes it possible to filter the measuring the sliding g₁.

The module 44 for calculating the temporal variation of sliding Δ_(g1)comprises a memory 62 which can store an initial filtered sliding valueg_(1i) produced by the module 42 when the unit 34 is started up. Thus, atriggering device 64 can assure storing the current sliding valueproduced by the module 42 when the unit is started up.

The module 44 additionally comprises a subtracter 66 which can calculatethe difference between the current filtered sliding g₁ obtained at theoutput from the module 42 and the initial filtered sliding value g_(1i)stored in the memory 62. A sliding variation Δ_(g1)=g₁−g_(1i) in thestand 16A is thus obtained.

In this embodiment, the unit 46 can assure the regulation of therelative correcting speed of the unit 34. In theory this gain is −1.

An additional correction signal u_(2A)=−1*Δ_(g1) is thus obtained at theoutput from the module 46.

As illustrated in FIG. 1, the output of the unit 46 is connected to amultiplier 69A which is provided at the output of the speed regulator30A. The output of the multiplier supplies the speed command value u_(A)to the drive motor of the rolls 18. The multiplier can multiply thecommand value u_(3A) by (1+u_(2A)). Thus, the percentage of the speedcommand u_(1A) is increased or decreased by a quantity equal to theopposite of the variation of sliding Δ_(g1) at the point of measurementconcerned.

It has been found that an installation of this type makes it possible toassure improved regularity of the thickness of the strip at the outputof the rolling installation. In fact, the additional correction u_(2A)which is provided by the unit 34 makes it possible to take into accountin the running of the installation variations of sliding which occur inparticular in the first stand, by acting directly on this stand.

The additional correction carried out by the unit 34 is satisfactorysince it is possible to prove that the variation of sliding in a standis equal to the relative variation of thickness in the following stand,i.e.:

$\frac{\Delta \; E_{2}}{E_{2}} = {\Delta \; g_{1}}$

where:

-   -   ΔE₂ is the variation of thickness at the output from the stand        16B;    -   E₂ is the reference thickness at the output from the stand 16B;    -   Δg₁ is the variation of sliding at the output from the stand.

FIG. 3 illustrates another embodiment of a rolling installation. Thisincludes elements which are identical or correspond to those in FIG. 1.These are designated by the same reference numbers.

This installation additionally comprises a sensor 138 for measuring thespeed V_(c2) of rotation of the drive motors of the stand 16B, thusmaking it possible to measure the instantaneous circumferential speed ofthe work rolls of the second stand 16B. This sensor is connected to theadditional compensation unit 34.

In this embodiment, the unit 34 comprises two outputs, one which isconnected to the multiplier 69A and a second one which is connected to asecond multiplier 69B which is integrated into the speed regulator 30B.

The second output of the additional compensation unit 34 can provide anadditional correction u_(2B) sent to the multiplier 69B in order toprovide at the output thereof a speed command value u_(B) which isapplied to the motor of the second stand 16B.

The command u_(B) is equal to the approximate command u_(tB) correctedby the additional correction u_(2B) according to the ratiou_(B)=U_(tB)(1+u_(2B)).

In addition, the additional compensation unit 34 comprises an outputu_(2c) for controlling the gripping position of the rolls of the thirdstand 16C.

The diagram of the additional correction unit 34 is illustrated in FIG.4. This diagram contains once again the modules 42 and 44 of the firstembodiment.

In addition, the unit 34 comprises a module 70 for estimating thetransfer time of the product between the second and third stands 16B,16C. This module comprises a memory 72 for storing the distance d₂₃which separates the second and third stands 16B and 16C, as well as anestimator 74 for estimating the linear speed V_(S2) of the strip betweenthe second and third stands 16B, 16C. This estimator 74 can determine bycalculation the speed of the strip at the output from the second stand16B, in particular on the basis of the ratio:

V _(s2) =V _(c2)(1+g _(S2Th))

where:

-   -   V_(s2) is the linear speed of the strip between the second and        third stands; and    -   V_(c2) is the circumferential speed of the work rolls of the        second stand obtained from the sensor 138;    -   g_(S2Th) is the theoretical sliding at the output from the        second stand.

The module 70 comprises a divider 76 which can calculate the time t₂₃ oftransfer of a point of the strip B between the second and third stands,from the distance d₂₃ which separates these stands and the speed V_(S2)of circulation of the strip.

At the output from the divider 76 there is provided an adder 78 which isconnected to a memory 80 for storing a delay constant τ corresponding tothe time of propagation of the sliding filter 58.

The output of the module 70 is connected to a delay line 82 which isintegrated into the correction module 46. This delay line receives atthe input the signal −Δg₁ obtained at the output from the multiplier 68.

The delay line 82 can assure application of an additional correctionsignal u_(2A), u_(2B) to the stands 16A and 16B with the delay producedby the module 70.

The output from the delay line 82 is applied to the two multipliers 69A,69B such that the speed commands u_(A), u_(B) are each correctedrelatively as a percentage of a quantity equal to:

−Δg₁(t+t₂₃−τ)

where:

-   -   t is the measurement instant;    -   t₂₃ is the time of transfer between the stands 16A and 16B; and    -   τ is the propagation time of the sliding filter 58.

The role of the module 47 is to assure maintaining the traction betweenthe stands 16B and 16C by calculating correcting gripping u_(2c) for thestand 16C on the basis of the speed correction u_(2B). In fact, thespeed correction u_(2B) on the one hand and the variation of thicknessat the input of the stand 16C generated by the variation of sliding Δg₁on the other hand give rise to these variations of traction. The outputfrom the module 82 is filtered by the module 90 in order to assureadaptation of the dynamics of the motor of the stand 16B relative to thegripping of the stand 16C. A gain G₉₁ is applied by a module 91 to theoutput signal of the module 90, in order to ensure that the variation ofposition of the gripping u_(2c) of the stand 16C is just sufficient tocompensate for the variation of traction induced by u_(2B).

The gain of the module 91 is given by the ratio:

$G_{91} = {\frac{\frac{\partial F_{3}}{\partial E_{e}}}{{Cg}_{3}}E_{e\; 3}}$${{where}\text{:}} - \frac{\partial F_{3}}{\partial E_{e}}$

is the variation of effort of the stand 16C relative to the variation ofthickness at the input of this stand; and

-   -   Cg₃ is the yielding of the stand 16C; and    -   E_(e3) is the thickness at the input of the stand 16C.

In the example illustrated in relation to FIGS. 3 and 4, the first andsecond stands have their roll rotation speed corrected in order to takeinto account variations of sliding Δg₁ at the output from the firststand, so that the variation of thickness which may have taken place atthe output from the second stand relative to a theoretical optimumthickness is compensated for during the passage of the strip into thethird stand 16C.

More generally, the method according to the invention can be extended tomore than two successive stands, the speed of the rolls of all thestands or only of a partial number of stands, with the exception of thefinal one, being able to be corrected by the same relative amount, andtaking into account the transfer time of the product between the secondstand and the final corrected stand, so that the final corrected standassures compensation for the variation of thickness generated by thevariations of sliding at the output from the first stand.

Advantageously, and as illustrated in FIGS. 1 and 3, the inertiacompensation unit 32 additionally receives the speed correction u_(1A)of the regulator 30A as is habitually known, and the additional speedcorrection u_(2A) obtained by taking into account the correcting theunit 34, such that the variations of delivery at the input of the stand16A can be compensated for by means of the system for maintaining thetraction at the input of the rolling mill, with the purpose of notdisrupting the traction at the input of the stand 16A.

In the embodiment illustrated, the units 30A, 30B and 34 are separate.However, as a variant, these units are put into operation functionallyby a single computer.

In the embodiment previously described, the corrections of the speeds ofthe stands are applied starting from the first stand. However, in a dualmanner, these stand speed corrections can be applied starting from thefinal stand. For example, for a rolling mill with five stands:

-   -   only a correcting relative speed equal to +Δg₁(t+t₂₃+t₃₄+t₄₅−τ)        is applied to the final stand 16E; or    -   correcting relative speed equal to +Δg₁(t+t₂₃+t₃₄−τ) is applied        to the two final stands 16D and 16E; or    -   correcting relative speed equal to +Δg₁(t+t₂₃−τ) is applied to        the three final stands 16C, 16D, 16E.

In the preceding formulae, the following notations are used:

-   -   t is the instant of measurement;    -   t₂₃ is the transfer time between the stands 16B and 16C;    -   t₃₄ is the transfer time between the stands 16C and 16D;    -   t₄₅ is the transfer time between the stands 16D and 16E;    -   τ is the propagation time of the sliding filter 58.

In this embodiment, the inertia compensations are applied to the coilerdevice.

1-13. (canceled)
 14. A method for controlling cold rolling of a sheetmetal strip, including continuous cold passage of the strip into atleast two successive stands, each stand including at least two drivenrolls between which the strip circulates and is compressed, the methodcomprising the steps of: estimating a variation of sliding at the outputfrom one of the at least two successive stands; and correcting a speedof rotation of the at least two driven rolls of the one stand and/or afurther stand of the at least two successive stands, corrected inaccordance with the estimated variation of sliding.
 15. The methodaccording to claim 14 wherein estimating the variation of slidingincludes measuring a linear speed of the strip at the output from theone stand, estimating a circumferential speed of the driven rolls in theone stand, and calculating a sliding of the strip based on the linearspeed of the strip at the output from the one stand and thecircumferential speed of the rolls of the one stand.
 16. The methodaccording to claim 14 wherein the variation of sliding is estimated forthe one stand, taking into consideration a direction of circulation ofthe strip.
 17. The method according to claim 14 wherein the step ofcorrecting a speed is applied to a set of the at least two successivestands, taking into consideration a direction of circulation of thestrip.
 18. The method according to claim 17 wherein corrections of speedapplied to the at least two successive stands are identical.
 19. Themethod according to claim 14 wherein correcting a speed includes varyingthe speed of the one stand and/or the further stand which is correctedwhen estimating a variation of sliding.
 20. The method according toclaim 14 wherein correcting a speed includes varying a speed of the onestand corrected with temporal offsetting, the temporal offsetting beingequal to a time of transfer of the strip between the further correctedstand and a following stand, taking into consideration the direction ofcirculation of the strip.
 21. The method according to claim 20 whereinthe temporal offsetting includes a delay caused by filtering.
 22. Themethod according to claim 14 wherein correcting a speed includes varyinga speed of a first stand corrected with temporal offsetting, thetemporal offsetting being equal to the time of transfer of the stripbetween a stand following the one stand where the variation of slidingis estimated and the first corrected stand, taking into considerationthe direction of circulation of the strip.
 23. The method according toclaim 14 further comprising the step of applying a gripping correctionto at least one stand adjacent to a corrected stand, in order tomaintain the traction.
 24. The method according to claim 14 furthercomprising the step of controlling a traction maintenance deviceupstream from the one stand, the controlling taking into account theestimated variation of sliding.
 25. A device for controlling coldrolling of a sheet metal strip including at least two successive stands,each stand including at least two driven rolls between which the sheetmetal strip circulates in cold conditions and is compressed, the devicecomprising: means for estimating a variation of sliding at an outputfrom at least one stand; means for correcting a speed of rotation of theat least two driven rolls of at least one stand corrected in accordancewith the estimated variation of sliding; and means for implementing amethod according claim
 14. 26. A device for controlling cold rolling ofa sheet metal strip including at least two successive stands, each standincluding at least two driven rolls between which the sheet metal stripcirculates in cold conditions and is compressed, the device comprising:an estimator for estimating a variation of sliding at an output from atleast one stand; a regulator for correcting a speed of rotation of theat least two driven rolls of at least one stand corrected in accordancewith the estimated variation of sliding; and a computer for implementinga method according claim
 14. 27. A method for controlling a thickness ofa cold-rolled sheet metal strip, including continuous cold passage ofthe strip into at least two successive stands, each stand including atleast two driven rolls between which the strip circulates and iscompressed, the method comprising the steps of: estimating a variationof sliding at the output from one of the at least two successive stands;and correcting a speed of rotation of the at least two driven rolls ofthe one stand and/or a further stand of the at least two successivestands, corrected in accordance with the estimated variation of sliding.28. The method according to claim 27 wherein estimating the variation ofsliding includes measuring a linear speed of the strip at the outputfrom the one stand, estimating a circumferential speed of the drivenrolls in the one stand, and calculating a sliding of the strip based onthe linear speed of the strip at the output from the one stand and thecircumferential speed of the rolls of the one stand.
 29. The methodaccording to claim 27 wherein the variation of sliding is estimated forthe one stand, taking into consideration a direction of circulation ofthe strip.
 30. The method according to claim 27 wherein the step ofcorrecting a speed is applied to a set of the at least two successivestands, taking into consideration a direction of circulation of thestrip.
 31. The method according to claim 30 wherein corrections of speedapplied to the at least two successive stands are identical.
 32. Themethod according to claim 27 wherein correcting a speed includes varyingthe speed of the one stand and/or the further stand which is correctedwhen estimating a variation of sliding.
 33. The method according toclaim 27 wherein correcting a speed includes varying a speed of the onestand corrected with temporal offsetting, the temporal offsetting beingequal to a time of transfer of the strip between the further correctedstand and a following stand, taking into consideration the direction ofcirculation of the strip.
 34. The method according to claim 33 whereinthe temporal offsetting includes a delay caused by filtering.
 35. Themethod according to claim 34 wherein correcting a speed includes varyinga speed of a first stand corrected with temporal offsetting, thetemporal offsetting being equal to the time of transfer of the stripbetween a stand following the one stand where the variation of slidingis estimated and the first corrected stand, taking into considerationthe direction of circulation of the strip.
 36. The method according toclaim 27 further comprising the step of applying a gripping correctionto at least one stand adjacent to a corrected stand, in order tomaintain the traction.
 37. The method according to claim 27 furthercomprising the step of controlling a traction maintenance deviceupstream from the one stand, the controlling taking into account theestimated variation of sliding.
 38. A device for controlling coldrolling of a sheet metal strip including at least two successive stands,each stand including at least two driven rolls between which the sheetmetal strip circulates in cold conditions and is compressed, the devicecomprising: means for estimating a variation of sliding at an outputfrom at least one stand; means for correcting a speed of rotation of theat least two driven rolls of at least one stand corrected in accordancewith the estimated variation of sliding; and means for implementing amethod according claim
 27. 39. A device for controlling cold rolling ofa sheet metal strip including at least two successive stands, each standincluding at least two driven rolls between which the sheet metal stripcirculates in cold conditions and is compressed, the device comprising:an estimator for estimating a variation of sliding at an output from atleast one stand; a regulator for correcting a speed of rotation of theat least two driven rolls of at least one stand corrected in accordancewith the estimated variation of sliding; and a computer for implementinga method according claim 27.